Tacrolimus or FK-506, the active ingredient in PROGRAF (tacrolimus capsules and injections, Astellas Pharma US, Inc. Deerfield, Ill.), is a macrolide immunosuppressant produced from Streptomyces tsukubaensis. Tacrolimus is used along with other medications to prevent rejection (attack of a transplanted organ by the immune system of a person receiving the organ) in people who have received kidney, liver, or heart transplants. Tacrolimus is in a class of medications called immunosuppressants. It works by decreasing the activity of the immune system to prevent it from attacking the transplanted organ. Tacrolimus has been found to be a safe drug for use during pregnancy in transplant patients (Laifer. S. A. and Guido, R. S. Mayo Clin Proc (1995) 70:38894; Jain et al. Transplantation (1997) 64:55965). Tacrolimus (FK506) has been shown to suppress overt diabetes in 84% of treated NOD mice, a model for Type 1 diabetes, at younger age (Kurasawa et al. Clin Imm Immuno Ther (1990) 57:274-279). In 1991, a clinical study with tacrolimus (0.15 mg/kg BID) was initiated in patients with type I diabetes (Carroll et al., Transplant Proc. 1991 December; 23(6):3351-3). While the initial response of five patients was disclosed as “encouraging” (Carroll et al., Transplant Proc. 1991 December; 23(6):3351-3), published results were inconclusive and no further data from this clinical study or further clinical studies have been published.